key error when building dict with arrays

Question

I am trying to build two dicts, one with even street values and one with odd street values. Each street has a Ref_ID, and I want each dict to use these values as the keys and their corresponding sequence numbers as the values.

I saw a former post to make a dict with an array as the values: append multiple values for one key in Python dictionary

I tried doing this in my code although I think the conditionals for even and odd as well as using an arcpy.SearchCursor is adding some complexity to the code:

import arcpy

#service location layer
fc = r"J:\Workspace\FAN3 sequencing3\gisdb\layers.gdb\Rts_239_241_314_GoLive"

# create variables

f1 = "Route"
f2 = "Ref_ID"
f3 = "Sequence"
f4 = "Street_Number"

# create containers

rSet = set()
eLinks = dict()
oLinks = dict()

# make a route list

with arcpy.da.SearchCursor(fc, f1) as cursor:
    for row in cursor:
        rSet.add(row[0])
    del row

# list of even side street sequences
eItems = []
eCheckStreet = []

# list of odd side street sequences
oItems = []
oCheckStreet = []

# make two dicts, one with links as keys holding sequence values for the even side of the street
# the other for the odd side of the street

for route in rSet:
    with arcpy.da.SearchCursor(fc, [f2,f3,f4]) as cursor:
        for row in cursor:
            if row[2] != '0' and int(row[2]) % 2 == 0:
                if row[0] in eLinks:
                    eLinks[str(row[0])].append(row[1])
                else:
                    eLinks[str(row[0])] = [row[0]]
            elif row[2] != '0' and int(row[2]) % 2 != 0:
                if row[0] in eLinks:
                    oLinks[str(row[0])].append(row[1])
                else:
                    oLinks[str(row[0])] = [row[0]]
        del row

print eLinks, oLinks

The output is the Ref_ID as both the key and the value. I've tried changing the index just to see if I'd getting soemthing different but it's still the same. I also tried converting if str(row[0]) in eLinks but to no avail.

I don't know if this will fix the problem, but after `elif` your `if` is looking for `row[0]` in `eLinks`, while it should probably look in `oLinks`. That will always return `False`. You might want to make both `eLinks` and `oLinks` `defaultdict(list)`, so that you don't have to initialize manually (i.e. you can skip the nested `if`s). — Mikk, Jan 31 '17 at 22:45
Thanks Mikk for pointing out the oLinks typo. I changed that and used collections but got the same result. I then got rid of the nested if and it worked like a charm. Go ahead and post the answer and I'll check it off. Thanks! — geoJshaun, Jan 31 '17 at 23:18
Actually, I thuink you should answer your own question, I'm not 100% sure about what you did :-) — Mikk, Jan 31 '17 at 23:32
I used the collections.defaultdict(list) and got rid of the nested if, as you suggested. — geoJshaun, Jan 31 '17 at 23:44

score 0 · Accepted Answer · answered Feb 01 '17 at 16:07

The issue is likely in the nested if and how those conditions interplay with each other. You don't have to take on your shoulders the responsibility of standard key checks on your dictionary: there's a built-in data structure for your that does that: collections.defaultdict: https://docs.python.org/2/library/collections.html#collections.defaultdict

import arcpy
from collections import defaultdict

#service location layer
fc = r"J:\Workspace\FAN3 sequencing3\gisdb\layers.gdb\Rts_239_241_314_GoLive"

# create variables

f1 = "Route"
f2 = "Ref_ID"
f3 = "Sequence"
f4 = "Street_Number"

# create containers

rSet = set()
eLinks = defaultdict(list)
oLinks = defaultdict(list)

# make a route list

with arcpy.da.SearchCursor(fc, f1) as cursor:
    for row in cursor:
        rSet.add(row[0])
    del row


# make two dicts, one with links as keys holding sequence values for the even side of the street
# the other for the odd side of the street

for route in rSet:
    with arcpy.da.SearchCursor(fc, [f2,f3,f4]) as cursor:
        for row in cursor:
            if row[2] != '0' and int(row[2]) % 2 == 0:
                eLinks[str(row[0])].append(row[1])
            elif row[2] != '0' and int(row[2]) % 2 != 0:
                oLinks[str(row[0])].append(row[1])
        del row
print eLinks, oLinks

key error when building dict with arrays

1 Answers1